This application is co-pending with my three other patent applications, Ser. Nos. 720,314; 720,485; and 720,490 and having the same filing date of Sept. 3, 1976; related to the various aspects of the expander engine.
This invention relates to an expander engine of Wankel type and more particularly to a low noise, high power, light weight and compact expander engine for use primarily in underwater propulsion systems operating with either an open cycle or a closed thermal cycle.
Underwater propulsions systems are generally of three types: a turbine, a reciprocating expander, and an electrical motor battery.
A turbine is basically a steady state machine of high power to weight ratio and high speeds. However, its limitations include high sensitivity of its efficiency to off design speed conditions which must exist in a multi-speed vehicle or require a high ratio variable speed transmission and/or a higher specific fuel consumption at off design than would be required for expander type engines.
The reciprocating expanders presently being used are of the "barrel" configuration with cylinders driving either a cam or swash-plate orientated so that their cylinders move parallel to the axis of the vehicle. Their main disadvantages are that the acceleration of the pistons generates a vibratory force in the most adverse direction and the noise projected as a result seriously limits the vehicles acoustic capabilities. Furthermore, masses of the pistons cannot be perfectly balanced in the axial direction, except by providing opposed cylinders which makes the engine a complicated and large system.
The electric motor battery systems use several types of motors with or without speed reducers and several types of energy sources. However, their main disadvantages include the fact that their power to weight ratio is higher than that of either of the above-mentioned thermal systems and the cost per unit power is also higher. Futhermore, their volume to power ratio is much higher than that for the other two systems.
The use of a Wankel type expander for torpedo or underwater propulsion has been considered previously as described in Pierce et al's, U.S. Pat. No. 3,744,940, assigned to Curtiss-Wright Corporation. The configuration described therein is a Wankel engine operating with pressurized vapor from an external source. The vapor is delivered through two valves for over 90.degree. of crank rotation driven by timing gears causing valve speed to be 0.5 crank shaft speed. These valves are external to the chamber. The crank is driven by a three-lobed rotor which is also rotating in the same direction as and at one third the speed of the crank. The rotor is driven by the expansion of the working vapors delivered to the two-lobed cavities of the stationary chamber. This arrangement makes it difficult to deliver the vapors from an external source without adversely affecting the clearance volume of the engine and hence its performance. Furthermore, this arrangement also results in an unbalanced force from the eccentrically located center of mass of the rotor which must be balanced by eccentric masses attached to the opposite ends of the crank shaft.
It is thus desirable to provide a low noise, high power, light weight and compact expander engine which has the best features of both the turbine engine and the Wankel type engine by virtue of its special features and where all rotating masses rotate about their respective centers of mass and rotation is in a plane perpendicular to the axis of the vehicle, thus, minimizing vibration and noise in the most preferential direction.